1. Field of the Invention
The invention relates to a multi-casting communication system including mobile communication terminals, a server used for the multi-casting communication system, a method of making multi-casting communication, and a program for causing a server to make multi-casting communication, and more particularly to a multi-casting communication system including mobile phones each having a function of “push to talk over cellular” (hereinafter, referred to as “PoC”) or personal data assistances (hereinafter, referred to as “PDA”) having a function of making communication, a server used for the multi-casting communication system, a method of making multi-casting communication, and a program for causing a server to make multi-casting communication.
2. Description of the Related Art
One of functions a related mobile communication terminal has is a “PoC” function. The PoC function means a function allows a plurality of members joining to a group through a PoC server to make multi-casting communication by half-duplex communication through his/her mobile communication terminal as if they make conversation by means of a transceiver.
The PoC function is much characterized in accomplishing multi-casting communication by making half-duplex communication. While multi-casting communication is being made, when one of members joining to a group through a PoC server speaks (in particular, when he/she makes voice communication), other members are not allowed to speak the one of members finishes speaking.
Consequently, it is not clear to others as to who wants to speak next or who will speak next, resulting in that smooth conversation cannot be made.
That is, a related mobile communication terminal is accompanied with a problem that while one of members belonging to a certain conversation session is speaking by means of a PoC function, other members can listen to his/her words, but cannot speak, and accordingly, if a plurality of members belongs to a conversation session, it is not obvious to others as to who will speak next, resulting in that some of the members simultaneously actuate a PoC switch of his/her mobile communication terminal in order to speak next.
In order to avoid such a problem as mentioned above, some attempts have been made to make obvious who will speak next, when a plurality of members uses a PoC function of his/her own mobile communication terminals.
For instance, Japanese Patent Application Publication No. 2000-513526 (patent reference 1) has suggested a method of controlling accesses.
In the suggested method, when a first user who is allowed to make communication is making conversation through a remote unit in a dispatch system allowing a user to make communication with a plurality of other users, if a second user using another remote unit actuates a “push to talk” button (hereinafter, referred to as a “PTT” button) to break into the conversation, the second user is entitles to make conversation, if the second user at that time has a higher rank than a rank of the first user presently making conversation.
Japanese Patent Application Publication No. 2002-522988 (patent reference 2) has suggested a system for determining a speaking order in an audio conference accomplished by a computer network.
In the suggested system, when a user requests joining conversation in a computer-networked audio conference, a conference server adds the user's request into a waiting list equipped in the conference server. The conference server keeps judging whether the user's request is a top in the waiting list, and allows the user to start conversation, if the user's request is judged to be a top in the waiting list.
Thus, a combination of the method suggested in the patent reference 1 and the system suggested in the patent reference 2 would provide a dispatch system in which when a user requests joining conversation, he/she actuates a PTT button to inform a server of his/her request, and the server, if a user transmitting a request thereto has a higher rank than a rank of a user presently making conversation, allows the user to break into the conversation, but if a user transmitting a request thereto has a rank equal to or lower than a rank of a user presently making conversation, adds the user's request into a waiting list. When a user finishes making conversation, the server allows a user listed on a top of the waiting list to start conversation.    Patent Reference 1: Japanese Patent Application Publication No. 2000-513526 (pages 11 and 22, FIGS. 3A and 3B) (based on PCT/US97/10832)    Patent Reference 2: Japanese Patent Application Publication No. 2002-522988 (pages 15 and 43) (based on PCT/US99/18549)
However, even if the method suggested in the patent reference 1 were combined with the system suggested in the patent reference 2, a priority for joining conversation would be determined arbitrarily. In other words, a priority for joining conversation is not always optimally determined in accordance with the system.
Furthermore, it is not obvious to members belonging to a conversation session as to who is entitled to speak next, resulting in that a conversation session is not smoothly made.
In addition, since a priority for joining conversation is a predetermined fixed order, the above-mentioned combination system is accompanied with a problem that even if a user needs to speak for an urgent reason, he/she cannot join conversation.
Japanese Patent Application Publication No. 2001-188740 (published on July 2001) has suggested an electronic conference system in which a server preferentially provides a right to speak to a user who is in charge of a chairman among a plurality of users, and provides a right to speak to other users in dependence on proceeding of a conference. If a first user speaks to a second user, the server provides a right to speak next, to the second user.
Japanese Patent Application Publication No. 8-505990 (published on June 1996) which is based on PCT/FI94/00034 has suggested a conference system in which a priority is assigned to a speech theme, and a speech signal transmitted from a user having a highest priority among all of users is transmitted to all of users.